Several U.S. banks were hit with online attacks over the past few months, but it's been unclear who was responsible. Now, government officials and security researchers are saying Iran was waging these cyberattacks, according to a report by the New York Times.

"There is no doubt within the U.S. government that Iran is behind these attacks," James A. Lewis, a former official in the State and Commerce departments and a computer security expert at the Center for Strategic and International Studies in Washington, told the Times.

The attacks were aimed at several major banks, including Wells Fargo, J.P. Morgan Chase, Bank of America, Citigroup, HSBC, and others. They involved inundating the banks' Web sites with bogus traffic, known as distributed denial-of-service attacks.

"The amount of bandwidth that is flooding the websites is very large, much larger than in other attacks, and in a sense unprecedented," chief executive of private security firm CrowdStrike Dmitri Alperovitch told the Wall Street Journal in September.

Apparently, it was the huge amount of traffic, along with the know-how to carry out these types of attacks, that convinced U.S. government officials that attacks were coming from Iran. These officials, however, have not provided any technical evidence to back up their claims.

While the cyberattacks were an inconvenience to both the banks and their customers, no private data or information was known to be stolen. According to the New York Times, security experts said this is further proof that the DDoS attacks were state-sponsored.

An unknown group called the "cyber fighters of Izz ad-din Al qassam" has claimed responsibility for the attacks -- saying that it was retaliating for the release of the controversial video posted to YouTube that mocked the Prophet Mohammad. The group has warned that the attacks would continue until the video was removed from "the Internet." However, according to the New York Times, officials now believe that Izz ad-din Al qassam was actually a cover for Iran.

The U.S. and Iran have a strained relationship, to say the least. The U.S. government has placed sanctions on Iran for years. In November, the U.S. State Department announced that it was sanctioning several Iranian groups and individuals for restricting Internet freedom and creating an "electronic curtain" that cut off its citizens from the rest of the world. The U.S. has also reportedly waged its own cyberattacks against Iranian power plants, oil companies, and nuclear facilities with three viruses called Flame, Stuxnet, and Duqu.

Izz ad-din Al qassam has also promised to stay the course with its attacks. "Rulers and officials of American banks must expect our massive attacks!" the group wrote in a Pastebin post last week. "From now on, none of the U.S. banks will be safe from our attacks."

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Dara Kerr is a staff reporter for CNET focused on the sharing economy and tech culture. She grew up in Colorado where she developed an affinity for collecting fool's gold and spirit animals.
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